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Atomic structure III: Modern atomic theory
Section 1
Rutherford model: where do electrons reside?
Problem:
Electromagnetic spectrum : Light travels as ….
Waves have a Wavelength -
and a frequency -
Short wavelength = __________ frequency and ___________ energy
colors:
Longer wavelength = __________ frequency and ___________ energy colors:
Continuous spectrum –
Bright line spectrum –
BL spectrum is the element’s “ fingerprint” –
How did Kirchhoff know that he’d discovered a new element from viewing sun’s corona spectrum?
Flame tests:
Examples:
How can the bright line spectrum be explained?
Draw the absorption
and emission of energy here:
Electron shells –
Electron Ground state –
Excited electron state
Light is emitted when…
Color of light corresponds to …
Atomic spectra is many colors because…
Other examples of excited state elements:
1) How do we know that electrons orbit in shells?
If Rutherford was correct:
If Bohr is correct:
2) Why do electrons orbit in shells? HDYK?
Quantum Theory: Max Planck (1900)
Quantized energy –
One quantum of light energy is called a ….
Bohr Model (Niels Bohr 1913)
Energy levels –
Higher energy levels (shells) =
vs. lower energy levels (shells) =
Learning Check:
1. What is the source of the bright line spectrum of an element?
2. How does the ground state and excited state of an atom compare in terms of energy?
3. What determines the color of the light in an individual bright line?
4. In what way is an atomic spectrum (bright line spectrum) like a fingerprint? How is it useful?
Section 2A
Bohr diagrams:
Ex: Aluminum
oxygen
Electron configuration
Rules:
Ex:
How many electrons occupy the 2nd energy level of a phosphorus atom in the ground state?
Valence electrons –
Kernal electrons –
Ex
Bohr diagrams :
Be
F
Na
P
Lewis (electron dot) symbols Ex: Hydrogen
Magnesium
Oxygen
chlorine
Draw the Lewis diagrams for Al and N
2-8-3
Al:
Al
2-8-8-7 N:
N
How does the number of outer electrons change within a group on the periodic table?
Within a period (row)?
Learning check:
1. Write the electron configuration for an atom of Ca in the ground state:
2. How many kernel and valence electrons does calcium have?
3. Which noble gas has a kernal like calcium?
4. Draw the Bohr diagram and Lewis electron dot symbols for Lithium, nitrogen and fluorine
Excited state electron configurations
Ex: Sketch the electron jumping from ground state to excited state
Li
C
F
1 As an electron in an atom moves from the ground state to the excited state, the electron
(1) gains energy as it moves to a higher energy level
(2) gains energy as it moves to a lower energy level
(3) loses energy as it moves to a higher energy level
(4) loses energy as it moves to a lower energy level
44 Which is an electron configuration for an atom of chlorine in the excited state? HDYK?
(1) 2–8–7
(2) 2–8–8
(3) 2–8–6–1
(4) 2–8–7–1
Section 2B
Periodic table – organized by…
fill in the table with electron configurations:
Why can’t the outer shell hold more than 8 electrons?
Learning check
1. A neutral Sulfur atom is in the ground state.
Without looking directly at the electron configuration determine:
a. the number of valence electrons
HDYK?
b. the number of occupied energy levels
c. the electron configuration
2. A neutral atom has the ground state electron configuration of 2-8-8.
HDYK?
a. What group and period is it located in? HDYK?
b. What properties will it have?
Section 3
Modern view of the atom: Wave Mechanical model
What electron waves are allowed?
Arrangement of electrons in atoms
Orbital : Region of …
1st shell has _____ Sublevel with one orbital holds _____ e-’s
2nd shell has an ____ sublevel with one orbital holds _____ e-’s
PLUS a _____ sublevel with 3 orbitals that holds _____ e-’s
for a total of ____ e-’s
Test your learning
1. The modern model of the atom is sometimes called the wave mechanical model. What does the name infer?
2. How is an orbital different from an orbit?
3. On modern periodic tables, the alkali metals and alkaline earth metals (groups 1 and 2) are in the “S” block,
while groups 13 through 18 are in the “P” block. Write an hypothesis for why this might be so.
Why does the periodic table have such a weird shape?